Magnetic phase control of electrical space discharge devices



Aug. 11, 1.942. v w. P. ovERBEcK 2,292,397

MAGNETIC PHASEl CONTROL OF ELECTRICAL SPACE DISCHARGE DEVICES Filed Jan`. l2, 1938 L y f @ELI l I. W/cox P OVERBECK Patented Aug. 11,

FFICE MAGNETIC PHASE CONTROL F ELECTRI- CAL SPACE DISCHARGE DEVICES wuwx r. Overbeek, Waltham, Raytheon Manufacturing a corporation of Delaware Mass., assigner to Company, Newton,

Application. January 12, 1938, Serial No. 184,617

3 Claims.

This invention relates to phase control of electrical space discharge devices, and more particularly to such control as applied to an electrical space discharge device in which the starting of the current is determined by means of an elec- -tromagnetically energized control element.

In electrical gaseous discharge tubes in which the current output is controlled by varying the phase angle at which the current starts to flow upon the application of an alternating voltage to such a tube, it is often desirable to control the current down to zero and up to its maximum value. It is also desirable to produce an arrangement so that at one point in the variation of the control element an abrupt change of the current from zero to its maximum value or from its maximum value to zero occurs. With previous arrangements using an electrostatlcally-controlled grid for determining the starting of current, it has been theoretically impossible to produce these results completely. Even where such results were approximated, it was necessary to resort to the use 'of movable contacts and complicated and massive arrangements. In order for a grid-controlled tube to produce the desired results, it is necessary to shift the phase of the control voltage through a value of zero degrees or 180 degrees. In a simple phase-shifting circuit using a resistance and a reactance, one of which is variable, it is necessary for the variable element to reach a limit of either zero or infinity in order to produce the desired results. A lsimple variable inductance or condenser cannot accomplish either of these results and still cover a suiciently large variation to perform useful control, while with a variable resistance it is impossible to approach either zero or infinity uniformly, and the point of zero current cannot be passed through without an abrupt change from zero to infinite resistance which necessarily means the use of electrical contacts or some other complicated system.`

One of the objects of my invention, therefore, is to produce a control for a gaseous discharge device so as to control the average current output through its zero value and its maximum value without the use of electrical contacts or complicated and massive equipment.

Another object is to provide means for controlling through zero the phase angle at which the control element of such a device causes .conduction of current to star A still further object is to provide an arrangement in which by means of a small continuouslyvariable impedance, an abrupt change from zero to maximum current output may be obtained.

The foregoing and other objects of my invention Will be best understood from the following description of exemplifications of my invention,

referencebeing had to the diagrammatic drawing, wherein:

Fig 1 is a circuit diagram illustrating one embodiment of my invention;

Fig. 1a represents a variation of the arrangement shown in Fig. 1;

Fig. 2 is a vector diagram representing the operation of the circuit of Fig. l:

Fig. 2a is a vector diagram representing the operation of the circuit of Fig. la; and

Fig. 3 is a curve showing the relationship between the output current of my device and the phase between the control factors and the anode voltage.

'I'he control is preferably utilized in a magnetically-controlled tube shown at l in Fig. 1. 'I'his tube is of the type which is fully described and claimed in the copending application of Percy L. Spencer, Serial No. 612,235, filed May 19, 1932, for an improvement in Electrical gaseous discharge devices. The tube l consists of an envelope 2 containing an anode 3 and an indirectlyheated cathode 4 which may be raised to temperature of thermionic emission by means of a heating filament 2li;V Surrounding the discharge space between the cathode 4 and-the anode 3 is an auxiliary electrode 5 which may consist of a metal cylinder, either perforate or imperforate. Instead of completely surrounding the discharge space, the auxiliary electrode 5 may partially surround it. The elevelope 2 is filled with a suitable ionizing gas or vapor, preferably with argon at a pressure of the order of one millimeter c1' less. The auxiliary electrode 5 is connected to the cathode 4 by means of the conductor 6. In order to control the starting'cf the current between the cathode 4 and the anode 3, a control winding l wound uponra magnetic core 2l is provided. The magnetic core 2l has pole pieces which impress a transverse magnetic field across the discharge path within the auxiliary electrode 5. In parallel with the winding 'l is connected a condenser 8. The condenser 8 is preferably selected of such a size as to make the parallel ci'rcuit resonant at the frequency of the voltage applied thereto. A magnetically-controlled tube of the type described above operates so that when a positive voltage is impressed upon the anode, starting of current between the cathode and anode will be delayed until the magnetic field created by the control magnet falls to a predetermined minimum value. In many instances this value may be substantially zero. l

In order to supply the device with power, transformer 9 is provided. The transformer 9 has a primary l0 which may be connected to a suitable source of alternating current and a secondary Il. One end of the secondary Il is connected by means of a conductor I2 through a load I3 to the anode 3. The other end of the secmediate the resistance tent, and in this way vector is Es,

ondary winding Il is connected by means of a cond ctor Il to the cathode I.

In' order to supply the control winding 1 with current, a phase-shifting circuit consisting of a resistance in series with an inductance It is connected between the conductors I2 and/'I l. Either the resistance I or the inductance IB, or both, may be adjustable.` provided with a tap I1 intermediate its ends. Preferably this tap is located at the central point on the winding I I. A conductor Il extends from the tap I1 to one end of-the control coil 1, while a conductor I9 extends from the point interthe other end of said control coil. When the transformer! is energized and either the resistance I5 or iductance I6, or both, are varied, the time at which the current starts between the cathode 4 and the anode t in each alternating current cycle is delayed to a predetermined ex- .the amount of current or power delivered to the load I3 is controlled.

In order to analyze the operation of the circuit as illustrated in Fig. 1, the resistance I5 is represented by the symbol R, the inductance I6 is represented by the symbol L, the voltage between the upper end of the secondary winding I'I and the tapv I1 isrepresented by Et, the voltage between the lower end of the secondary winding II and the tap I1 is represented by Ee, the total voltage across the secondary winding I I is represented by E., and the voltage across the control coil 1 is represented by Ee., The current whichy flows through the resistance I5 `and inductance I6 is represented by I; The vector diagram shown in Fig. 2 utilizes the various quantities so designated, and illustrates the operation of the arrangement as shown in Fig. 1.

As will be noted in Fig. 2, the long horizontal while Ee being in phase with E! is represented by a horizontal vector of half the length of El. If R and L are adjusted so that L predominates, a current I1 which lags the voltage E. mayilow through the series RL circuit. The current I1 will produce through theresistance, a voltage drop of 11R in phase with the current. This current will also produce a voltage drop LX through the'inductance. This latter voltage drop will be at right angles to the current I1. As illustrated in Fig. 2, the sum of 11R and 11X must equal the voltage Es. The voltage which appears across the control winding 1 may then be determined by the vector Eer extending from the end of the vector E: to the intersection of the two vectors 11R and 11X. If the resistance R is increased or the inductance L is decreased so as to bring the current `I more nearly into phase with the voltage El. a current Iz may flow through the series RL circuit. This current will produce the voltage drops 12R and 12X in the relationship as shown, whereupon the control voltage Ee: will appear across the control winding 1. The large solid semi-circle in Fig. 2. represents the locus of the end of the vector Ec as the currentv I is varied from 90 degrees out of phase with the vector Es into a condition in which it is in phase with said voltage. The arrow on said solid The secondary winding isv I5 and inductance I6 to.

semi-circle represents the direction in which the vector Ee is shifted as R is increased or as L is decreased. Changing the direction of variation of these quantities will change the direction in which the vector Ee is shifted. The dotted circle and the arrow thereon represent similarly the direction in which the end of the vector I is shifted as the quantities R. and L are varied.

In any series circuit, such as is represented in Fig. 1, it is substantiall'y'impossible to obtain a current exactly in phase or entirely out of phase with the voltage impressed across the ends of such a circuit. However. a phase shift of the order of magnitude as illustrated in Fig. 2 can very easily be secured. It will'be seen that such a phase shift varies the vector Ee through a considerable range, and further that this vector is shifted through a phase angle of degrees with respect to the horizontal voltages.

In Fig. 3 is represented the manner in which the current output from the tube I varies as the variations described in connection with Fig. 2 are produced. Along the horlzontal'axis at the top of Fig. 3 is plotted the phase angle of the flux which is set up by the control winding 1 with respect to the voltage E. impressed between the cathode l and the anode 3. When the flux is in phase with the voltage E., its value is substantially zero at the time the anode voltage passes through zero, and therefore conduction of current will occur substantially throughout the entire period that the anode remains positive. Under these conditions the maximum amount of current will 4flow through the output circuit. Since the operation of the magnetic field upon the discharge is independent of the direction of that iield, the in-phase condition of the flux may be represented either as a value of zero degrees or as degrees. However, as the flux is shifted more and more out of vphase with the applied voltage, the starting of the current is delayed to a greater and greater extent until the point is reached at which the flux is displaced 180 de vgrees with respect to the applied voltage when starting of the tube is prevented entirely. lUnder these conditions, zero current flows in the load. From the foregoing it will be seen that at the value of 180 degrees or zero degrees, the current through the load is either zero or a maximum. This means that in a practical device as the phase angle of the ux with respect to the applied voltage approaches 180 degrees, the current output approaches zero, and as the flux passes through a value of 180 degrees, the current jumps suddenly from zero to -the maximum value. The flux of the control magnet 2l is in phase with the current which flows through the coil 1, and this current lags the voltage Ee applied to said winding 1 by substantially 90 degrees. Thus the phase along the horizontal axis at the bottom of Fig. 3 on which the phase angles are displaced 90 degrees with respect to those along the upper horizontal axis. Under these conditions the curve represents accurately the manner in which the current through the load will vary as the phase angle of Ec varies with respect to E, as illustrated in the vector diagram of Fig. 2. As pointed out above in connection with Fig. 2, it is a comparatively simply matter to shift the vector Ec through a value of 90 degrees with respect to the voltage Es. Therefore, it is a comparatively easy matter to obtain the type of control as represented in the vicinity of 90 degrees on the lower horizontal axis. It will be seen at this point that a continuous and smooth control of the current output can'be secured down to a zero value, the same ltype of control can be secured up to a maximum value, and a sudden transition from zero to maximum current output can be produced by shifting the control voltage Ee through the angle of Ec with respect to E; is plotted f said tube may 2,292,397 vwere assumed, including the fact that the parallel circuit consisting of the coil 1 and the condenser 8 should .draw no current. Since this parallel circuit is resonant to the applied voltage, this is theoretically true. Moreover, I have found that if the impedance of the parallel circuit is three times the value of the resistance R or more, there is no appreciable deviation from the analysis as given above. Furthermore, an arrangement as represented in Fig. l actually performs without any substantial variation in the manner as analyzed in Figs. 2 and 3.

Instead of using an inductance in series with the resistance l5, a condenser could be used as illustrated in Fig. la. In Fig. la the reference numerals correspond to identical parts in Fig. l. The condenser is represented at 22. In Fig. 1a either the resistance R or the condenser C, or both, may be varied.

The analysis of the variation of Fig. l, as illustrated in Fig. la, is given by the vector diagram of Fig. 2a. In this gure the various vectors are marked exactly in the same manner in connection with Fig. 2. It will be noted that the only difference is the fact that in Fig. 2a the current vectors lead the voltages Et and Es, and therefore the voltage drops are of opposite phase with respect to those shown in Fig. 2. In Fig. 2a the control voltage Ec likewise is of opposite phase with respect to the voltage Ec of Fig. 2. The curve of Fig. 3, however, applies directly to the operation of Fig. la inasmuch, as has been previously pointed out, as the control of the discharge through the tube is independent of the control ux and is dependent only on the magnitude phase of said flux.

In any two-element phase shift circuit, suchv as illustrated .in Fig. 1 or Fig. la, the maximum rate of change of change in impedance occurs at the point where both impedances are equal in magnitude. This condition represents a phase shift of Ec with re-l spect to Es of 90 degrees. It is in the region of this value of phase shift that many of the objects of my invention are accomplished. In any practical system it fs easy to construct impedances which are equal, and therefore by my arrangementthe controlis made easiest at the point where the desired results are to be produced.

' Of course it is understood that this invention is not limited to the particular details as described above inasmuch as many equivalents will suggest themselves to those skilled in the art. For example, instead of using the particular magnetic control tube described, any tube in which the starting of current is controlled by a magnetic field could be constructed to utilize the principles of my invention. Furthermore, it will be seen that one of the fundamental features of my invention is the production of a phase shift between the control voltage and the current which flows through the control circuit. Therefore, any tube in which the starting oi' that tube is made responsive to the ilow of current through a control circuit likewise could be made to utilize the principles of my invention. Since the electrical circuit of the control coil l is separate from that of the tube I, the voltage impressed across be any proportion of the secondary Il or may be supplied to said tube by a separate transformer or transformer winding.v If desired the condenser 8 may be omitted and the analysis given holds good provided the impedance phase angle with respect to of 1 remains more than three times the impedence of i5. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed:

1. In combination. a source of alternating current voltage including a transformer having a transformer winding, a tap on said transformer winding intermediate the ends thereof, a gas or vapor-lled space discharge device provided with electrodes, means for impressing across said electrodes an alternating current voltage in phase with the voltage across said transformer winding, electromagnetically-energized control means for controlling the starting of current flow between said electrodes, a phase-shifting circuit comprising a resistance and a reactance connected in series between the ends of said secondary winding, one of said irnpedances being variable, and means for impressing on said control means for energizing the same the voltage appearing between said intermediate tap and the point intermediate said resistance and impedance.

2. In combination, a source of alternating current voltage including a transformer having a transformer winding, a tap on said transformer winding intermediate the ends thereof, a gas or vapor-filled space discharge device provided with electrodes, means for impressing across said electrodes an alternating current voltage in phase with the voltage across said transformer winding, control means for controlling the starting of current flow between said electrodes, a control circuit associated with said control means, said control means being responsive to current iiowing through said control circuit, a phase-shifting circuit comprising a resistance and a reactance connected iriseries between the ends of said secondary winding, one of said impedances being variable, means for impressing on said control circuit the voltage appearing between said intermediate tap and the point intermediate said resistance and impedance, and means in said control circuit for producing a substantial phase`\ displacement between said last-named voltage\ and the current flowing in said control circuit.

3. In combination, a source of alternating current voltage including a transformer having a transformer winding, a tap on said transformer winding intermediate the ends thereof, a gas or vapor-filled space discharge device provided with electrodes, means for impressing across said electrodes an alternating current voltage in phase with the voltage across said transformer winding,

' electromagnetic control means for controlling the starting of current ilow between said electrodes, a control circuit associated with said control means, said control means current flowing through said control circuit, a phase-shifting circuit compris/ing a resistance and a reactance connected in series between the ends of said secondary winding, one of said impedances being variable, means tween said intermediate tap and the point intermediate said resistance and impedance, and means in said control circuit for producing a substantial phase displacement 'between said last-named voltage and the current flowing in said control circuit. i

WILCOX P. OVERBECK.

being responsive to for impressing `on said ,control circuit the voltage appearing be- 

